Cisco WAN :: Dual Internet Fail Over On 1812 Router?

I am simply trying to configure fail over configuration in my 1812 router. I have done some configuration on my router but my configuration is not working as i want. My router does not goes to secondary route until i unplug the primary interface cable on my router. when i unplug the primary cable it goes to secondary route and then i plug back primary cable the router come back to primary link.so my configuration is working when my primary gateway down but it is not working when internet goes down from isp end. i have attached my running configuration.